The cause of osteoporosis are multifactorial; these include aging, immobilization, genetic fsctor, initial bone mass, nulliparity, postmenopause, cigarette, etc. Among them the hormonal factors are very important. It is worthwhile to study the effects of various hormones on bne cells. Authors evaluated the effects of TGB-B, 17-B estradiol, insulin, and human growth hormone as a stimulatory factors, and r-interferon as a inhibitory factor on the MC3T3 osteoblast cells with measurement of cell numbers, osteocalcin and 3[H]-thymidine incorporation. 1. TGF-B was a potent stimulator on ostoblast with increased change in cell morphology (number, size, shape), osteoclacin level and 3[H]-thymidine incorporation in dose depen- dant fashion. 2. 17-B estradiol was also a potent stimulator on osteoblast activity as well as TGF-B except osteoclacin level which w#as not shown in dose dependant fashion. 3. There were little changes on osteoblast with insulin, growth hormone, and r-interferon. Through this study it is confirmed that TGF-B and 17-B estradiol showed marked stimulatory effect on osteoblast cell in vitro.